Dynamical processes in a multi-motor gear drive of heavy slabbing mill

A real case study is represented of abrupt failures in a new multi-motor gear drive of vertical rolls in the heavy slabbing mill. Modal analysis is conducted, and the lowest torsional vibration modes are verified by the data from an industrial plant. Conditions of parametric resonances due to variable stiffness of teeth are determined within the range of working speed. The branched gear drive is investigated by the non-linear dynamical model with backlashes. It is shown that instantaneous dynamic loads in driveline are strongly dependent on the difference in gap sizes and phase shift between two intermediate gears in the output gear wheel coupling. Deviation in electrical parameters by 0.5 % is considered as the additional cause of not equal load sharing of parallel motors. Results of this research allowed preventing further failures of the gearbox and optimizing slabbing mill control. The proposed approach can be used in other multi-motor machines

Vibration-Based Diagnostics of Radial Clearances and Bolts Loosening in the Bearing Supports of the Heavy-Duty Gearboxes

The problem solved in this research is the diagnosis of the radial clearances in bearing supports and the loosening of fastening bolts due to their plastic elongation (creep) or weak tightening using vibration signals. This is an important issue for the maintenance of the heavy-duty gearboxes of powerful mining machines and rolling mills working in non-stationary regimes. Based on a comprehensive overview of bolted joint diagnostic methods, a solution to this problem based on a developed nonlinear dynamical model of bearing supports is proposed. Diagnostic rules are developed by comparing the changes of natural frequency and its harmonics, the amplitudes and phases of shaft transient oscillations. Then, the vibration signals are measured on real gearboxes while the torque is increasing in the transmission during several series of industrial trials under changing bearings and bolts conditions. In parallel, dynamical torque is measured and its interrelation with vibration is determined. It is concluded that the radial clearances are the most influencing factors among the failure parameters in heavy-duty gearboxes of industrial machines working under impulsive and step-like loading. The developed diagnostics algorithm allows condition monitoring of bearings and fastening bolts, allowing one to undertake timely maintenance actions to prevent failures

Studying the Influence of the Impact Gap Value on the Average Translational Speed of the Wheeled Vibration-Driven Robot

The general design of the wheeled vibration-driven robot is developed in the SolidWorks software (Dassault Systèmes SolidWorks Corporation, Premium 2022, Waltham, MA, USA) on the basis of a double-mass semidefinite oscillatory system. The idea of implementing the vibro-impact working regimes of the internal (disturbing) body is considered. The corresponding mathematical model describing the robot motion conditions is derived using Euler-Lagrange equations. The numerical modeling is carried out by solving the obtained system of differential equations with the help of the Runge-Kutta methods in the Mathematica software (Wolfram Research, Inc., 13.0, Champaign, IL, USA). The computer simulation of the robot motion is conducted in the MapleSim (Waterloo Maple Inc., 2019.1., Waterloo, ON, Canada) and SolidWorks software under different robot design parameters and friction conditions. The experimental prototype of the wheeled vibration-driven robot is developed at the Vibroengineering Laboratory of Lviv Polytechnic National University. The corresponding experimental investigations are carried out in order to verify the correctness of the obtained results of the numerical modeling and computer simulation. All the results are presented in the form of time dependencies of the robot’s basic kinematic characteristics: displacements, velocities, accelerations of the wheeled platform and disturbing body. The influence of the impact gap value on the average translational speed of the robot’s wheeled platform is studied, and the corresponding recommendations for designers and researchers of similar robotic systems are stated. The prospective directions of further investigations on the subject of the present paper and similar vibration-driven locomotion systems are considered

Dynamic Analysis of an Enhanced Multi-Frequency Inertial Exciter for Industrial Vibrating Machines

Multi-frequency vibrators have advantages in bulk materials processing but their design is usually complicated. This article presents the synthesis of design parameters of a two-frequency inertial vibrator according to the specified power characteristics. Based on the developed mathematical model, the parameters of variable periodic force is derived for two angular velocities 157, 314 rad/s and their ratios 0.5 and 2. In the case of the 0.5 ratio, the instant angular velocity of the resulting force vector is 2.0–3.5 times greater than for ratio 2. A dynamical model of vibrating screen with the synthesized inertial drive is considered. It was found that at the ratio of angular velocities 0.5, the second harmonic of acceleration prevails at 50 Hz, while at the ratio of 2, the first harmonic has a greater amplitude at 25 Hz. For the first variant, the power does not depend on the initial angle between unbalances, and at the second variant, it can vary. The angle of rotation of unbalances affects the trajectory of the centre of mass and the phases of the harmonics but does not affect their amplitude. Due to such dynamical features, the two-motor inertial drive allows the vibrating machines to operate at a wider range of frequencies and amplitudes

Review of Linear Electric Motor Hammers—An Energy-Saving and Eco-Friendly Solution in Industry

Standard hydraulic breaking hammers are widely used for crushing oversized blasted materials and concrete structures demolition in industry. These hammers, installed in on-surface working excavators or stationary manipulators at the dumping points of underground conveyors, provide the required limited sizes of bulk materials and enable the safe operation of other equipment (screens, crushers). In parallel, hydraulic hammers have an alternative—fully electric hammers. This paper aims to review existing linear electric motor (LEM) hammers as an energy-saving and eco-friendly solution in industry. Global market analysis is presented with potential branches of LEM hammers. Several aspects for implementation—design optimization, dynamics simulation, machine control, and performance estimation—are considered. Different case studies for LEM-hammer application are given. The preliminary measurements are demonstrated on the electric hammer of Lekatech Company, which is intended for the mining industry and construction demolition. Experiments showed that depending on the impact frequency, type of rock, and shape of the crushing tool, the time to fracture varies significantly. Optimal parameters exist for every case, for which adjusting requires online hammer control

Increasing the Wear Resistance of Structural Alloy Steel 38CrNi3MoV Subjected to Isothermal Hardening and Deep Cryogenic Treatment

In the production of critical parts for various machines and mechanisms, expensive structural steels are used alloyed with chromium, nickel, molybdenum, and vanadium. In practice, the wear resistance of parts, especially under severe operating conditions, may be insufficient due to uneven microstructure and the content of retained austenite. Therefore, increasing the operational stability of various products made of alloy steels is an important task. The purpose of this work is to investigate the effect of isothermal hardening from the intermediate (γ+α)-area and the duration of deep cryogenic treatment on the structure formation and frictional wear resistance of 38CrNi3MoV steel. The isothermal hardening promotes the formation of the required multiphase microstructure of 38CrNi3MoV steel. The influence of the duration of deep cryogenic treatment on the microhardness, amount of retained austenite, fine structure parameters, and friction wear of 38CrNi3MoV steel are established. Complex heat treatment of 38CrNi3MoV steel, according to the proposed mode, makes it possible to achieve a significant decomposition of retained austenite to martensite, which leads to an increase in frictional wear resistance of ~58%

Condition Monitoring of Horizontal Sieving Screens—A Case Study of Inertial Vibrator Bearing Failure in Calcium Carbonate Production Plant

Predictive maintenance is increasingly popular in many branches, as well as in the mining industry; however, there is a lack of spectacular examples of its practice efficiency. Close collaboration between Omya Group and Wroclaw University of Science and Technology allowed investigation of the failure of the inertial vibrator’s bearing. The signals of vibration are captured from the sieving screen just before bearing failure and right after repair, when it was visually inspected after replacement. The additional complication was introduced by the loss of stable attachment of the vibrator’s shield, which produced great periodical excitation in each place of measurement on the machine. Such anomalies in the signals, in addition to falling pieces of material, made impossible the diagnostics by standard methods. However, the implementation of advanced signal processing techniques such as time–frequency diagrams, envelope spectrum, cyclic spectral coherence, orbits analysis, and phase space plots allowed to undermine defects (pitting on the inner ring). After repair, the amplitudes of vibration from the damaged bearing side were reduced by five times, while sound pressure was only two times lower. The quantitative parameters of vibrations showed significant changes: time series RMS (−68%) median energy of spectrograms (89%), frequencies ratio of cyclic spectral coherence (−85%), and average amplitude of harmonics in envelope spectrum (−80%). The orbits demonstrated changes in inclination angle (16%) and sizes (−48, … −96%), as well as phase space plots sizes (−28, … −67%). Directions of further research are considered

The experimental study of compaction parameters and elastic after-effect of fine fraction raw materials

Mining and metallurgical enterprises generate a significant amount of secondary raw material resources having small-fractions (below 3 mm). A significant volume of these materials can be returned into the production process by the use of the briquetting method. The quality of briquettes, in particular, their strength, is significantly affected by a phenomenon called elastic after-effect. For a theoretical study of the elastic after-effect influence on the quality of the briquettes, taking into account the pressing tool configuration, experimental data are obtained for three materials (peat, kaolin and manganese concentrate). Results are in creating the analytical relations (regression models) having enough high accuracy to describe the dependence of compaction coefficient, elastic after-effect, density and elastic heave (decompaction) on an external pressure in the compaction machine

On the Dynamics of an Enhanced Coaxial Inertial Exciter for Vibratory Machines

Theoretical investigations into the capabilities of a coaxial inertial drive with various operating modes for vibratory conveyors and screens are conducted in the paper. The coaxial inertial exciter is designed with one asynchronous electric motor and the kinematically synchronized rotation of two unbalanced masses. Three variants of angular speeds ratios, namely ω2/ω1 = 1, ω2/ω1 = –1, and ω2/ω1 = 2, are considered. Based on these relations, the circular, elliptical, and complex motion trajectories of the working members are implemented. In the first two cases, single-frequency harmonic oscillations take place. In the latter case, the double-frequency periodic oscillations are excited. The dynamic behavior of the motor’s shaft during its running-up and running-out is considered. The influence of the inertial parameters of the unbalanced rotors and the relative phase shift angle between them on the elliptical trajectories of the vibratory system’s mass center motion is investigated. The use of forced kinematic synchronization provides the motion stability of the vibratory system for all considered working regimes